1. Field of the Invention
The field of art to which the present invention pertains is the treatment of sour petroleum distillates or fractions, the treatment being commonly referred to as sweetening. More specifically, the present invention relates to a metal chelate mercaptan oxidation catalyst having an average particle size of less than about 110 mesh.
2. Information Disclosure
Processes for the treatment of a sour petroleum distillate wherein said distillate is treated, in the presence of an oxidizing agent at alkaline reaction conditions, with a supported metal phthalocyanine catalyst dispersed on a fixed bed in a treating or reaction zone, have become well known and widely accepted in the industry. The treating process is typically designed to effect the catalytic oxidation of offensive mercaptans contained in the sour petroleum distillate with the formation of innocuous disulfides. Gasoline, including natural, straight run and cracked gasolines, is the most frequently treated sour petroleum distillate. Other sour petroleum distillates include the normally gaseous petroleum fraction as well as naphtha, kerosene, jet fuel, fuel oil and the like.
A commonly used continuous process for treating sour petroleum distillates entails treating the distillate in contact with a metal phthalocyanine catalyst dispersed in an aqueous caustic solution to yield a doctor sweet product. The sour distillate and the catalyst-containing aqueous caustic solution provide a liquid-liquid system wherein mercaptans are converted to disulfides at the interface of the immiscible solutions in the presence of an oxidizing agent--usually air. Sour petroleum distillates containing more difficultly oxidizable mercaptans are more effectively treated in contact with a metal phthalocyanine catalyst disposed on a high surface area adsorptive support--usually a metal phthalocyanine on an activated charcoal. The distillate is treated in contact with the supported metal phthalocyanine catalyst at oxidation conditions in the presence of an alkaline agent. One such process is described in U.S. Pat. No. 2,988,500. The oxidizing agent is most often air admixed with the distillate to be treated, and the alkaline agent is most often an aqueous caustic solution charged continuously to the process or intermittently as required to maintain the catalyst in a caustic-wetted state.
In U.S. Pat. No. 2,988,500 (Gleim et al.), the solid catalyst particles were exemplified having a carrier size in the range of 30 to 40 mesh. In U.S. Pat. No. 3,408,287 (Urban et al.), the solid catalyst particles for sweetening sour hydrocarbons were exemplified having a carrier size in the range of 60 to 100 mesh. Generally, the prior art has taught that hydrocarbon sweetening catalyst is supported on relatively finely divided particles.
The prior art discloses that there are limitations on the ability to treat a sour petroleum distillate with a catalytic composite consisting of a metal phthalocyanine disposed on a carrier material. Various improvements have been developed to further enhance the sweetening ability including the use of certain additives in the distillate treating process.
The prior art does not disclose or suggest, however, that a sour mercaptan-containing hydrocarbon distillate may be more effectively treated by a method comprising contacting the distillate at oxidation conditions with a mercaptan oxidation catalyst and a solid carrier material having an average particle size of less than about 110 mesh. I have discovered surprising and unexpected results when utilizing a supported oxidation catalyst of the present invention having a particle size of less than about 110 mesh to sweeten hydrocarbon distillates.